Photocatalysts such as anatase type titanium oxide are known to exert antifouling effect to decompose organic materials under ultraviolet light irradiation, antibacterial activity and hydrophilicity. Additionally, nowadays, photocatalysts exerting a catalytic function under visible light irradiation are attracting attention.
Formation of the above-described photocatalyst layer on the surface of a member such as glass is frequently carried out by means of vacuum film formation methods including sputtering and vapor deposition, or reduced-pressure film-formation methods.
Provision of an undercoat layer between the substrate such as glass and the photocatalyst layer formed on the surface of the substrate has been proposed in Japanese Patent Application Publication No. 9-227167, Japanese Patent Application Publication No. 10-66878, Japanese Patent Application Publication No. 2000-312830, and Japanese Patent Application Publication No. 2001-205094.
Japanese Patent Application Publication No. 9-227167 discloses that a barrier layer is provided between a glass substrate and a photocatalytic composition (medium) which is formed on the surface of the substrate for the purpose of preventing function deterioration of the medium caused by alkali eluted from the glass, and proposes use of zirconium oxide, in particular, amorphous zirconium oxide as the barrier layer.
Japanese Patent Application Publication No. 10-66878 discloses that a photocatalyst film is formed on a substrate in a state where an undercoat film is interposed therebetween, and in particular, zirconium oxide is used as the undercoat film and titanium oxide is used as the photocatalyst film.
Japanese Patent Application Publication No. 2000-312830 discloses that a layer of a metal oxide such as zirconium oxide is interposed between a substrate (aluminum) and a photocatalyst layer so as to control oxygen diffusion from the photocatalyst layer to the substrate with the aid of the metal oxide layer.
Japanese Patent Application Publication No. 2001-205094 discloses zirconium oxide as a photocatalytic material and discloses that a titanium oxide layer is formed on the exterior of the zirconium oxide.
PCT International Publication (WO 02/40417) discloses that a high temperature stable type cubic or orthorhombic zirconium oxide layer is formed between a substrate and a titanium oxide layer.
When a photocatalyst layer is formed according to the above-described methods, there are cases where no photocatalytic function is exerted, or such a function is not exerted unless the thickness of the photocatalyst layer is made thick, which causes the reflectance of the article to become large and interference color to be generated, and thereby the compatibility of the preferable reflectance and color tone with the photocatalytic activity is hardly achieved. Also, there are drawbacks that when a high temperature stable type cubic or orthorhombic zirconium oxide layer needs to be formed, low heat resistance resin and the like cannot be used as a substrate, and photocatalytic members having a large size for use in construction and the like can be hardly obtained because it is technically difficult to heat large size substrates uniformly.